1. Field of the Invention
This invention relates to a tube support and baffle combination for use in a heat exchanger. More particularly this invention may be used to provide a combination tube support and fluid type baffle within a shell and tube type heat exchanger.
2. Description of the Prior Art
In a conventional tube and shell type chiller, refrigerant carrying tubes are mounted within a shell in heat exchange relationship with a fluid to be cooled passing through the shell. This fluid to be cooled is usually water, brine, ethylene glycol or some similar fluid used to transfer heat between the chiller and the area to be cooled. The chiller is typically the evaporator of the refrigeration system wherein liquid refrigerant is converted to a gaseous refrigerant absorbing heat from the fluid to be cooled in the process.
The tubes within the shell and tube type heat exchanger are typically secured by tube sheets in a spaced parallel arrangement so that the fluid to be cooled can be circulated among and around the tubes. In addition thereto baffles are inserted into the heat exchanger to direct the fluid to be cooled in a tortuous path through the heat exchanger. By circulating the fluid to be cooled through a tortuous path the fluid water side heat transfer coefficient is increased and the overall amount of heat transfer from the fluid to the refrigerant is likewise increased.
The problem with conventional baffles is that part of the fluid to be cooled bypasses the baffle between the baffle and the shell thereby short-circuiting the heat exchanger and simultaneously reducing the heat transfer coefficient since the fluid velocity through the tortuous path is decreased and the mean temperature difference is decreased. This by-pass effect is especially pronounced since the shell of the typical shell and tube type heat exchanger is a segment of a commercially available pipe. This pipe is made to a large tolerance range and consequently baffle fit is often sloppy depending upon where the internal diameter of the pipe falls within the tolerance range.
This short-circuit effect has not previously been significant since in a conventional water chiller the heat transfer rate from the refrigerant to the tube was the limiting heat transfer factor in the overall performance of the heat exchanger. However, with the enhanced heat transfer surfaces being developed for tubes such as internal finning, the heat transfer rate is now controlled by heat transfer factors from the tubes to the water. Consequently, the short-circuiting of water through the heat exchanger results in a decrease in the chiller heat transfer rate and efficiency.
Typical of the baffles presently being used in shell and tube type heat exchangers are those shown in U.S. Pat. No. 3,656,588 entitled "Self Positioning Baffle for Shell and Tube Heat Exchangers" and U.S. Pat. No. 3,958,630 entitled "Heat Exchanger Baffle Arrangement". In neither case is the problem of baffle bypass addressed or resolved.